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| -rw-r--r-- | src/gallium/docs/source/tgsi.rst | 35 |
1 files changed, 15 insertions, 20 deletions
diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst index 5068285aaee..d2d30b41d00 100644 --- a/src/gallium/docs/source/tgsi.rst +++ b/src/gallium/docs/source/tgsi.rst @@ -1583,48 +1583,43 @@ These opcodes are used for bit-level manipulation of integers. .. opcode:: IBFE - Signed Bitfield Extract - See SM5 instruction of the same name. Extracts a set of bits from the input, - and sign-extends them if the high bit of the extracted window is set. + Like GLSL bitfieldExtract. Extracts a set of bits from the input, and + sign-extends them if the high bit of the extracted window is set. Pseudocode:: def ibfe(value, offset, bits): - offset = offset & 0x1f - bits = bits & 0x1f + if offset < 0 or bits < 0 or offset + bits > 32: + return undefined if bits == 0: return 0 # Note: >> sign-extends - if width + offset < 32: - return (value << (32 - offset - bits)) >> (32 - bits) - else: - return value >> offset + return (value << (32 - offset - bits)) >> (32 - bits) .. opcode:: UBFE - Unsigned Bitfield Extract - See SM5 instruction of the same name. Extracts a set of bits from the input, - without any sign-extension. + Like GLSL bitfieldExtract. Extracts a set of bits from the input, without + any sign-extension. Pseudocode:: def ubfe(value, offset, bits): - offset = offset & 0x1f - bits = bits & 0x1f + if offset < 0 or bits < 0 or offset + bits > 32: + return undefined if bits == 0: return 0 # Note: >> does not sign-extend - if width + offset < 32: - return (value << (32 - offset - bits)) >> (32 - bits) - else: - return value >> offset + return (value << (32 - offset - bits)) >> (32 - bits) .. opcode:: BFI - Bitfield Insert - See SM5 instruction of the same name. Replaces a bit region of 'base' with - the low bits of 'insert'. + Like GLSL bitfieldInsert. Replaces a bit region of 'base' with the low bits + of 'insert'. Pseudocode:: def bfi(base, insert, offset, bits): - offset = offset & 0x1f - bits = bits & 0x1f + if offset < 0 or bits < 0 or offset + bits > 32: + return undefined + # << defined such that mask == ~0 when bits == 32, offset == 0 mask = ((1 << bits) - 1) << offset return ((insert << offset) & mask) | (base & ~mask) |